1. Field of Invention
The present invention relates to a filter module and to a method of manufacturing a hollow fiber membrane bundle having at least two concentrically arranged filter stages. The invention in particular relates to filter modules for hemodialysis, in particular to filter modules which integrally contain a plurality of filtration stages.
2. Description of the Prior Art
A plurality of filters are required for a number of therapeutic processes of extracorporeal blood purification. In these processes, blood is as a rule filtered or dialyzed at hollow fiber membranes of a filter module for purifying toxic metabolites. High demands are made in this respect on the fluids used for substitution or for dialysis to be able to be used in the therapeutic processes. Such fluids are provided in pouches licensed under drug law or are manufactured online by the extracorporeal blood treatment machines. To be able to ensure the microbiological purity in the online processes, these fluids have to run through one or two filtration stages before they may be used as replacement fluids in dialysis or as substitution fluids in blood filtration processes.
There have previously been endeavors to design the fluid circuits of extracorporeal blood treatment circuits more compact and to integrate them for disposable articles. Cassette systems for extracorporeal blood treatment have in particular been developed for which a plurality of functions for blood treatment and fluid treatment are integrated.
Developments have equally been promoted in the field of blood filters using hollow fiber membranes in which a plurality of filter stages have been integrated in a filter module.
EP 0 791 368 A2 shows a two-stage filter module for hemodiafiltration. In a first stage, inflowing substitution fluid penetrates into the interior of the hollow fiber membrane, is filtered in so doing and is mixed with blood in a blood chamber at the head end of the filter module. In a second stage, the diluted blood runs through the interior of the hollow fiber membranes and is dialyzed and filtrated in so doing.
DE 39 01 446 A1 describes a two-stage filter having a first stage in which dialysis fluid is directed into the interior of the hollow fiber membranes, passes through the membrane and is filtered in so doing. The filtrate of the first stage is directly directed into the second stage and there flows through the outer space of the hollow fiber membrane bundle as dialysis fluid.
DE 33 26 704 A1 shows a two-stage filter module in which the hollow fiber membrane bundles are concentrically arranged. Blood is filtered in an inner first filtration stage. In the second, surrounding filtration stage, blood is treated in substance exchange with dialysis fluid.